Plasma sterilization apparatus

ABSTRACT

In order to provide a plasma sterilization apparatus with high plasma generation efficiency, the apparatus includes first and second electrodes ( 3, 2 ), a first dielectric body layer ( 1 ), and an insulating spacer ( 6 ). The first dielectric body layer ( 1 ) is disposed between the first and second electrodes ( 3, 2 ). The insulating spacer ( 6 ) is disposed between the first electrode ( 3 ) and the first dielectric body layer ( 1 ). The insulating spacer ( 6 ) has a lower permittivity than a permittivity of the first dielectric body layer ( 1 ).

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP 2011-089366 filed on Apr. 13, 2011, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma sterilization apparatus thatinactivates a floating fungus in the air (hereinafter referred to as anairborne bacillus).

2. Description of the Related Art

There are high expectations for realization of regenerative medicine,which uses an artificially cultured cell and tissue to regeneratedamaged skin, corneas, organs and so on, so as to improve functionalrecovery of patients. The number of patients with the targeted diseasesis estimated to 20,000 for corneal regeneration alone. Thus realizationof this technology is desired. Participations of pharmaceuticalcompanies are actualized, and it is expected that the regenerativemedicine will make a new healthcare industry in the future.

Clinical research for regenerative medicine requires a biological cleanroom (hereinafter referred to as BCR), which allows asepticmanipulation. In order to maintain the indoor environment of BCR, it isnecessary to establish sterilization technique, and this is an importantissue. The conventional method for sterilizing inside BCR generallyemploys a method for sterilizing the whole indoor environment by reekingof formaldehyde inside the room. However, the formalin is harmful tohuman body because of as its carcinogenicity, for example. The use offormalin will be tend to be prohibited. In view of this, a sterilizationtechnique using ozone instead of formalin has been proposed. Ozonegeneration techniques are disclosed in, for example, Japanese PatentApplication Laid-Open Publication No. 1-242404 and Japanese PatentApplication Laid-Open Publication No. 2003-323964. Bactericidal methodsusing ozone are disclosed in, for example, Japanese Patent ApplicationLaid-Open Publication No. 2007-159821, Japanese Patent ApplicationLaid-Open Publication No. 2005-211095, and Japanese Patent ApplicationLaid-Open Publication No. 2008-289801.

SUMMARY OF THE INVENTION

In the sterilization in BCR, it is important to sterilize airbornebacillus so as to improve cleanness in the room. In order to study a newmethod for sterilizing the airborne bacillus in BCR, sterilizationmethods, which are generally used in a medical front or in a healthcaremanufacturer, have been surveyed. The results are categorized asfollows.

-   1) A filtration method using a HEPA filter or the like-   2) A radiation sterilization method using a radiation (such as    γ-ray), ultraviolet (with a wavelength of 254 nm), electron beam or    the like-   3) A gas sterilization method using Ethylene oxide gas, Hydrogen    peroxide or the like

As described above, various sterilization methods are available.However, it is probably difficult to apply these sterilization methodsto sterilization of airborne bacillus in BCR. For example, a filtrationmethod has difficulty in completely capturing floating bacilli that passthrough a filter. The filtration method also has difficulty insterilizing the captured bacilli in the filter. Thus, after a lapse oftime, the bacilli may scatter from the filter into the air again. Theradiation sterilization method provides weak sterilizing activity, thusrequiring irradiation to the target bacilli to be sterilized for sometens of minutes to some hours. The problem arises in process time. Thegas sterilization is harmful to human body similarly to the formalin andrequires degassing for some hours to one day. Thus use of the gassterilization tends to be avoided. In view of such background, a newsterilization method using plasma has been proposed as a newsterilization method that does not use harmful material and can processat low temperature and high speed.

First, plasma generating modules that generate ozone or the like havebeen surveyed regardless whether their intended purpose is sterilizationor not. As a result, the survey has found a generally knowndielectric-barrier system. The dielectric-barrier system is a plasmagenerating module that covers both a high-frequency electrode and anearth electrode with a dielectric body layer. This technique is alsoused for a plasma display panel (PDP) or the like. This technique isused in a wide range of use as a structure that provides low temperatureplasma at atmospheric pressure with relative ease. However, theconfiguration generates a large amount of an electric power that isreactive and does not contribute to the plasma generation (hereinafterreferred to as reactive power). Thus it is difficult to achieve powersaving.

Japanese Patent Application Laid-Open Publication No. 1-242404 disclosesa structure that covers only a high-frequency electrode with adielectric body layer and includes an earth electrode disposedimmediately above the high-frequency electrode. In view of this, itwould appear that concentrated electrical lines of force pass through aplasma generation space (hereinafter referred to as a space). Thisenhances the electrical field strength in the space, thus increasingefficiently of the plasma. Further, Japanese Patent ApplicationLaid-Open Publication No. 2003-323964 and Japanese Patent ApplicationLaid-Open Publication No. 2008-289801 disclose a structure that includesa high-frequency electrode and an earth electrode disposed to sandwich adielectric body layer. Thus structure has a discharge gap between thehigh-frequency electrode and the earth electrode. It would appear thatthis structure achieves a reduced reactive power passing through thedielectric body layer, compared with that of Japanese Patent ApplicationLaid-Open Publication No. 1-242404. This increases the electric fieldstrength in the space, thus ensuring high plasma generation efficiency.However, in the structures disclosed in Japanese Patent ApplicationLaid-Open Publication No. 1-242404, Japanese Patent ApplicationLaid-Open Publication No. 2003-323964, and Japanese Patent ApplicationLaid-Open Publication No. 2008-289801, it is necessary to choose adielectric body layer with a high permittivity to increase the electricfield strength in the space. In principle, reactive current flows insideof the dielectric body layer, which generates the reactive power. Inview of this, it would appear that there is a need for further improvingthe plasma generation efficiency.

Japanese Patent Application Laid-Open Publication No. 2007-159821 andJapanese Patent Application Laid-Open Publication No. 2005-211095disclose that when a sterilization using ozone is performed, increasingtemperature of bacilli in the sterilization improves sterilizationeffect. The above patent literatures disclose the methods that generateozone using plasma or the like, control the temperature inside achamber, to which the ozone is supplied, so as to heat the bacilli. Thisensures sterilization at high speed. However, heating inside the chamberusing ozone is insufficient and there is a need for improvement.

The present invention has been made in view of the above-describedcircumstances, and it is an object of the present invention to provide aplasma sterilization apparatus with high plasma generation efficiency.

According to one aspect of the present invention to achieve the abovepurpose, there is provided a plasma sterilization apparatus thatincludes first and second electrodes, a first dielectric body layer, andan insulating spacer. The first dielectric body layer is disposedbetween the first and second electrodes. The insulating spacer isdisposed between the first electrode and the first dielectric bodylayer. The insulating spacer has a lower permittivity than apermittivity of the first dielectric body layer.

According to another aspect of the present invention, there is provideda plasma sterilization apparatus that includes a plasma generatingportion and a flow path. The plasma generating portion includes firstand second electrodes, a first dielectric body layer, and an insulatingspacer. The first dielectric body layer is disposed between the firstand second electrodes. The insulating spacer is disposed between thefirst electrode and the first dielectric body layer. The insulatingspacer has a lower permittivity than a permittivity of the firstdielectric body layer. The flow path is configured to provide fluidincluding a processing target of bacillus to a plasma region generatedby the plasma generating portion. The flow path is arranged in an upperstream side of the plasma region such that the fluid cools the plasmagenerating portion.

With the present invention, an insulating spacer that has the lowerpermittivity than the permittivity of the dielectric body layer isdisposed between the earth electrode and the dielectric body layer ofthe plasma generating module. This configuration provides a plasmasterilization apparatus that reduces reactive power and achieves highplasma generation efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are schematic diagrams illustrating configurationsof conventional plasma generating modules;

FIGS. 2A, 2B, and 2C are explanatory diagrams of dischargecharacteristics of a plasma generating module;

FIGS. 3A, 3B, and 3C are schematic diagrams illustrating configurationsof plasma generating modules of plasma sterilization apparatusesaccording to a first embodiment;

FIGS. 4A, 4B, and 4C are schematic diagrams illustrating otherconfigurations of plasma generating modules of the plasma sterilizationapparatuses according to the first embodiment;

FIGS. 5A, 5B, and 5C are explanatory diagrams illustrating asterilization mechanism of oxygen radical;

FIG. 6 is a table of a sterilization effect of the oxygen radical;

FIG. 7 is a schematic diagram illustrating a configuration of a plasmasterilization apparatus according to a second embodiment; and

FIGS. 8A and 8B are schematic diagrams illustrating sterile particles ofthe plasma sterilization apparatus according to the second embodiment.

DESCRIPTION OF THE EMBODIMENTS

As a result of studying conventional plasma sterilization apparatuses bythe inventors, the followings have been found. A voltage applied forgenerating plasma provides a high electric field strength inside adielectric body layer disposed between a high frequency applyingelectrode and an earth electrode while the voltage provides an lowelectric field strength outside the dielectric body layer. The lowelectric field strength outside the dielectric body layer contributes toplasma generation. Thus there is a need for increasing the electricfield strength outside the dielectric body layer in order to improveplasma generation efficiency. As a result of studying a method toachieve this, the inventors have thought of providing a seconddielectric body layer (an insulating spacer) between the earth electrodeand the dielectric body layer that has a lower permittivity than that ofthe above dielectric body layer. The present invention has been made inview of the above-described circumstances. Embodiments of the presentinvention will be described in detail below.

[First Embodiment]

A first embodiment according to the present invention will be describedbelow with a result of a study on conventional plasma generatingmodules.

FIGS. 1A, 1B, and 1C are schematic diagrams illustrating theconfiguration of the conventional plasma generating modules. In a plasmagenerating module that generates sterile particles such as ozone, asillustrated in FIG. 1A, a structure of a dielectric-barrier system isgenerally known. The dielectric-barrier system covers both ahigh-frequency electrode 2 and an earth electrode 3 with a dielectricbody layer 1 (type 1). Type 1 is also used for a plasma display panel(PDP) or the like and is used in a wide range of use as a structure thatprovides a low temperature plasma at atmospheric pressure with relativeease.

Type 1 illustrated in FIG. 1A includes a portion where a distancebetween the high-frequency electrode 2 and the earth electrode 3 issmallest, that is, a region where concentrated electrical lines of forcepass through. This provides a region with a high electric field strengthinside the dielectric body layer 1. This causes a high reactive powerpassing through inside the dielectric body layer 1. On the other hand,plasma is generated by an electric field that leaks into a space throughthe dielectric body layer 1. In view of this, type 1 has a structurewith a low plasma generation efficiency. Here, a reference numeral 4designates a substrate, a reference numeral 5 designates ahigh-frequency power supply, a reference numeral 50 designates a plasmagenerating portion, and a reference numeral 60 designates a dischargegap. Identical reference numerals designate identical configurations.

FIG. 1B illustrates a structure that covers only the high-frequencyelectrode 2 with the dielectric body layer 1 and disposes the earthelectrode 3 immediately above the high-frequency electrode 2 (type 2).Type 2 provides highly concentrated electrical lines of force 10 passingthrough a space so as to improve electrical field strength in the space.This achieves a reduced reactive power compared with type 1, thusgenerating plasma efficiently. However, similarly to type 1, a regionwhere the electric field strength is highest is provided inside thedielectric body layer 1. Thus the plasma generation efficiency is notsufficient.

FIG. 1C illustrates a structure that includes a high-frequency electrode2 and an earth electrode 3 sandwiching a dielectric body layer 1 and hasa discharge gap between the high-frequency electrode 2 and the earthelectrode 3 (type 3). This structure provides a region where theelectric field strength is highest in the space. This further reducesreactive power than type 2 and increases the electric field strength inthe space, thus generating plasma efficiently.

FIGS. 2A, 2B, and 2C are explanatory diagrams of dischargecharacteristics of a plasma generating module. FIG. 2A illustrates adevice configuration for measuring the discharge characteristics. Adirect current (hereinafter referred to as DC) power supply supplies DCpower to an inverter with transformer. The inverter with transformerboosts the supplied DC power and supplies a High-frequency voltage Vppto the high-frequency electrode 2 side of the plasma generating module.At this time, DC current and voltage of the DC power supply and theHigh-frequency voltage Vpp are measured.

FIG. 2B illustrates a discharge characteristics of type 1 structure.Specifically, type 1 has a discharge gap of 100 μm and includes adielectric body layer 1 with a film thickness of 20 μm. The dielectricbody layer 1 is made of a soda glass with a relative permittivity ∈ of8. High-frequency voltage Vpp increases with increasing DC voltage, andthe discharge is then initiated when the high-frequency voltage Vppexceeds 3000 V. The DC current that flows before the dischargeinitiation is indicated as B region (0.13 A). This portion represents areactive power. “A” region represents the electric power that went inthe plasma itself.

FIG. 2C illustrates a discharge characteristics of type 3 structure.Specifically, type 3 has a discharge gap of 100 μm and includes adielectric body layer 1 with a film thickness of 100 μm. The dielectricbody layer 1 has a relative permittivity ∈ of 8. In order to increasevoltage resistance of the dielectric body film, the dielectric body filmis thicker than type 1 and the discharge is initiated when Vpp exceedsaround 2100 V. The structure is configured to have an increased electricfield strength in the space, compared with type 1. Thus plasma isgenerated with the low High-frequency voltage Vpp. This shows that thereactive current before the discharge initiation is 0.05 A. Thisreactive current is lower than a current of type 1.

FIGS. 3A, 3B, and 3C are schematic diagrams illustrating configurationsof plasma generating modules of plasma sterilization apparatusesaccording to the embodiment. FIG. 3A illustrates a first structureaccording to the embodiment. The first structure includes an insulatingspacer 6 with a low permittivity disposed between a dielectric bodylayer 1 and an earth electrode 3. The high-frequency power supply 5 mayemploy a frequency of 10 kHz to 100 kHz. This reduces a reactive powerflowing inside a dielectric body layer 1 further than type 3. This alsofacilitates the passing of electrical lines of force 10 in a space, thusreducing a discharge initiation voltage. If the insulating spacer 6 hasa function as an adhesive layer when an earth electrode 3 is formed onthe dielectric body layer 1, this configuration leads to both reducedreactive power and facilitated production. For example, a double sidedtape made of organic material may be used. The material and thethickness of the insulating spacer 6 is specifically determined based ona plasma etching condition (for example, a etching gas, temperature, andpressure) and etching tolerance. Plasma in the atmosphere does not causesputtering. This allows use of organic material. Instead of use of thedouble sided tape, patterning may be employed after forming a laminatedfilm made of a dielectric body layer with a low permittivity and anelectrode material layer.

FIG. 3B illustrates a second structure of the embodiment. A structurewith a narrow insulating spacer 6 further reduces the reactive powerthat flows between the high-frequency electrode 2 and the earthelectrode 3 through inside a dielectric body film. A space region of aninferior surface of the earth electrode 3 is allowed to be used as aplasma generation space. It is expected that there is an effect toincrease plasma generation volume. However, in the case where theinsulating spacer 6 has a too narrow width, the earth electrode 3 is notfirmly installed. Thus the width of the insulating spacer 6 ispreferably equal to or more than a half of the width of the earthelectrode 3.

FIG. 3C illustrates an exemplary type 2 structure to which an insulatingspacer 6 is applied. Disposing the insulating spacer 6 at a region wherean electrical field strength is largest reduces reactive power andimproves plasma generation efficiency further than type 2. However,compared with the first and second structures of the embodiment, thereactive power is still large.

Plasma sterilization apparatuses that include the plasma generatingmodules with the structures according to FIG. 3A to FIG. 3C were usedfor sterilization of the air in BCR. This showed that each of thestructures reduces electric power and increases plasma generationefficiency further than the conventional structures.

FIGS. 4A, 4B, and 4C are schematic diagrams illustrating otherconfigurations of the plasma generating modules according to theembodiment. “A” portion of the first structure according to theembodiment illustrated in FIG. 4A will be described by referring to FIG.4B and FIG. 4C in detail. FIG. 4B illustrates a structure that includesa projection on a side face of the earth electrode 3, which concentratesof an electric field at a distal end of the projection (anelectric-field-concentrating portion 70). This reduces a dischargeinitiation voltage. FIG. 4C illustrates a structure that includes aprotruding portion (an electric-field-concentrating portion 70) on theside face of the earth electrode 3, which concentrates an electricfield, similarly to FIG. 4B. This reduces a discharge initiationvoltage. Choose of the structures of FIG. 4B and FIG. 4C may bedetermined considering material or a producing method of the earthelectrode 3. Both structures are formed by a known dry etching.

Plasma sterilization apparatuses that include the plasma generatingmodules with the structures according to FIG. 4B and FIG. 4C were usedfor sterilization of the air in BCR. This showed that each of thestructures reduces electric power and increases plasma generationefficiency further than the structures according to FIG. 3A to FIG. 3C.

The embodiment that includes the second dielectric body layer (theinsulating spacer 6), which has a lower permittivity than the dielectricbody layer between the electrode and the dielectric body layer, providesthe plasma sterilization apparatus with high plasma generationefficiency. The electric field concentrating portions disposed on theside face of the electrode improve plasma generation efficiency.

[Second Embodiment]

A second embodiment according to the present invention will be describedbelow. Matters that are not described in this embodiment and describedin the first embodiment may be also applied to this embodiment unlessthe circumstances are exceptional. The embodiment employs the modulewith the configuration according to FIG. 3A.

FIGS. 5A, 5B, and 5C are explanatory diagrams illustrating asterilization mechanism of oxygen radical. It is known that the oxygenradical 22 has stronger oxidizing action than that of ozone and largesterilization effect. An experiment was carried out. The experimentirradiated Bacillus subtilis with the oxygen radical 22 generated byoxygen plasma. Bacillus subtilis (processing target of bacillus 21)(Geobacillus stearothermophilus, ATCC7953), which has the most toleranceto plasma sterilization. Bacillus subtilis is an indicator bacillus ofplasma sterilization.

The number of Bacillus subtilis (processing target of bacillus 21) is10⁶. This forms a colony (cluster) 80 as illustrated in FIG. 5A. ThusBacillus subtilis (processing target of bacillus 21) undergoes oxidizingsterilization by the oxygen radical 22 gradually from a surface layer90.

FIG. 5B illustrates an observational result of Bacillus subtilis(processing target of bacillus 21) observed through a scanning electronmicroscope (SEM) before plasma irradiation and after 10 min oxygenplasma irradiation. Oxygen plasma irradiation causes desorption ofelements such as carbon (C) and oxygen (O), which are components ofBacillus subtilis (processing target of bacillus 21) with the oxygenradical 22 including the oxygen plasma. This shrinks the diameter ofbacillus. The desorption results in destroying cell walls of Bacillussubtilis (processing target of bacillus 21). Then Bacillus subtilis(processing target of bacillus 21) are killed.

FIG. 5C illustrates a relationship between a irradiation time and a longaxis diameter of bacillus when Bacillus subtilis (processing target ofbacillus 21) is irradiated with the oxygen plasma. At this time,Bacillus subtilis (processing target of bacillus 21) is measured attemperatures of 30° C. and 87° C. As a result, this showed that Bacillussubtilis (processing target of bacillus 21) heated to the temperature of87° C. shrinks its diameter of bacillus faster. The reason is thatcarbon and oxygen in Bacillus subtilis (processing target of bacillus21) have a higher response rate at higher temperature to be removed bythe oxygen radical 22 in the oxygen plasma. Bacillus subtilis(processing target of bacillus 21) halts shrinking the diameter ofbacillus in the surface layer after the plasma irradiation time ofaround 10 min. It is because the oxygen radical 22 removes organicmaterial, and then inorganic material, which is inseparable, remains.These matters are also confirmed by Bacillus subtilis (processing targetof bacillus 21) used in this experiment, which keeps active at thetemperature of equal to or less than 100° C. and are not killed at thetemperature of 87° C. FIG. 6 is an explanatory diagram illustrating asterilization effect of the oxygen radical 22. Bacillus subtilis(processing target of bacillus 21) was determined to be active orinactive using a liquid culture medium (TSB culture medium) illustratedin FIG. 5A. The liquid culture medium includes a PH indicator(bromocresol purple). When Bacillus subtilis (processing target ofbacillus 21) is active, PH varies and then color of the liquid culturemedium varies. After the plasma irradiation, a culture for 24 hours at58° C. was carried out. A culture result of Bacillus subtilis(processing target of bacillus 21) irradiated with oxygen plasma isillustrated in FIG. 6. In the case where Bacillus subtilis (processingtarget of bacillus 21) was at the temperature of 87° C., it wasconfirmed that 10⁶ of Bacillus subtilis (processing target of bacillus21) were killed after the process time of 20 minutes. On the other hand,in the case where Bacillus subtilis (processing target of bacillus 21)is at the temperature of 30° C., killing Bacillus subtilis takes theprocess time of 30 minutes. This confirmed that increasing thetemperature of Bacillus subtilis (processing target of bacillus 21) atplasma irradiation or before plasma irradiation improves sterilizationeffect.

FIG. 7 is a schematic diagram illustrating a configuration of a plasmasterilization apparatus according to the embodiment. FIG. 7 illustratesa device configuration that preheats an air including an airbornebacillus (processing target of bacillus 21) and sterilizes with theoxygen radical 22. First, the plasma generating portion could be burntout at high temperature and thus needs to be cooled. In view of this, afan 101 intakes an air (at atmospheric pressure) including the airbornebacillus (processing target of bacillus 21) while cooling the plasmagenerating portion. This heats the air including the airborne bacillus(processing target of bacillus 21) using thermal radiation of the plasmagenerating portion. At this time, a radiating fin 102 is provided toeffectively transfer heat from the plasma generating portion to the airincluding the airborne bacillus (processing target of bacillus 21).Reference numeral 100 designates a housing, and a white arrow designatesa direction of airflow.

Then the heated air contacts the plasma 23 and is sterilized by sterileparticles in the plasma 23. As the sterile particles, the oxygen radical22, which is included in the plasma, has larger sterilization effectthan that of ozone, which is mainly generated outside the plasma. Thestructure guides the air to contact the plasma 23 directly. Bringing theair in directly contact with the plasma 23 allows the oxygen radical 22in the plasma 23 to have an action on the floating bacillus (processingtarget of bacillus 21) in the air. The principle will be described indetail referring to FIGS. 8A and 8B. This structure ensures cooling theplasma discharging portion and preheating the airborne bacillus(processing target of bacillus 21) without a freezing device and aheater. This structure allows use of the oxygen radical 22 as thesterile particles. This ensures sterilization at high speed with alow-cost configuration. The temperature of the heated air variesaccording to a plasma generating condition and an airflow rate. The airis heated to high temperature by increasing electric power input to theplasma sterilization apparatus while decreasing the airflow rate.

FIGS. 8A and 8B are schematic diagrams illustrating the sterileparticles generated in the plasma sterilization apparatus according tothe embodiment. When the oxygen radical 22 generated in the plasmadiffuses from a plasma generating region, three-body collision with theoxygen molecules occurs. This changes the oxygen radical 22 into ozone24. Thus, as illustrated in FIG. 8A, in the case where the flow pathheight h is far larger than the generating region of the plasma 23, theozone 24 are main sterile particles having action on the airbornebacillus (processing target of bacillus 21). On the other hand, asillustrated in FIG. 8B, in the case where the flow path height h iswithin the plasma generating region, the oxygen radical 22 are mainsterile particles having a action on the airborne bacillus (processingtarget of bacillus 21), which are expected to have large sterilizationeffect. In order to obtain the sterilization effect by the oxygenradical 22, when a length between both ends of the high-frequencyelectrode 2 and the earth electrode 3 is defined as a discharge lengthL, the flow path height h is preferably equal to or less than a half ofL (0<h≦(½)L).

The above plasma sterilization apparatus was used to sterilize the airin BCR. This achieved sterilization with low electric power at highspeed.

In the embodiment, the electrode contacting the plasma 23 is describedas the earth electrode 3, and the electrode protected by the dielectricbody layer 1 is described as the high-frequency electrode 2. This causesno influence on effects of the embodiment even if the positions of theboth electrodes are switched each other.

With the embodiment, the second dielectric body layer (the insulatingspacer 6) with a lower permittivity than that of the dielectric bodylayer between the electrode and the dielectric body layer provides theplasma sterilization apparatus with high plasma generation efficiency.In the plasma generating region, the height of the airflow path may beequal to or less than a half of the electrode distance. This ensuressterilization at high speed.

The above-described embodiment should not be construed in a limitingsense; any modifications are possible without changing the scope of thepresent invention. For example, the above embodiments are described indetail for ease of describing the present invention. The presentinvention is not limited to configurations that include the wholeelements described above. Replacement of a configuration of oneembodiment with a configuration of another embodiment is possible.Addition of a configuration of one embodiment to a configuration ofanother embodiment is also possible. Addition, removal, and replacementof a part of the configuration among the respective embodiments are alsopossible.

Industrial Applicability

The present invention is not limited to the application of sterilizationin BCR. Application of electrical home appliances such as an airconditioner and a refrigerator, which require to harmlessly sterilizethe airborne bacillus at low temperature and at high speed. In thepresent invention, the sterilization effect is described for theairborne bacillus (such as a true fungus and a bacteria) as target.Needless to say, an organism such as floating virus in the air may besterilized.

What is claimed is:
 1. A plasma sterilization apparatus comprising:first and second electrodes; a first dielectric body layer disposedbetween the first and second electrodes; and an insulating spacerdisposed between the first electrode and the first dielectric bodylayer, the insulating spacer having a lower permittivity than apermittivity of the first dielectric body layer, wherein: the insulatingspacer is arranged such that at least a portion of the first electrodeoverlaps with the insulating spacer, as viewed from above, and theinsulating spacer is arranged such that the second electrode does notoverlap with the insulating spacer, or such that only a portion of thesecond electrode overlaps with the insulating spacer, as viewed fromabove.
 2. The plasma sterilization apparatus according to claim 1,further comprising an electric power supply configured to supply analternating voltage between the first and second electrodes, wherein agap is disposed between the first and second electrodes as a dischargespace.
 3. The plasma sterilization apparatus according to claim 1,wherein the insulating spacer is configured to reduce a reactive power.4. The plasma sterilization apparatus according to claim 1, wherein thefirst electrode includes a projection on a side face of the firstelectrode so as to reduce a discharge initiation voltage when generatingplasma.
 5. The plasma sterilization apparatus according to claim 1,wherein the insulating spacer is made of an organic material.
 6. Theplasma sterilization apparatus according to claim 1, wherein theinsulating spacer includes a double sided tape.
 7. The plasmasterilization apparatus according to claim 1, wherein the insulatingspacer has a width equal to or more than a half of a width of the firstelectrode.